function clearField(field) {
     // Check if field contains the default value
     if (field.value == field.defaultValue) {
          // It does, so clear the field
          field.value = "";
     }
}

function checkField(field) {
     // Check if user has entered information in the field
     if (field.value == "") {
          // User has not entered anything
          field.value = field.defaultValue;
     }
}